This application is based on application No. 37269/1998 filed in Japan, the contents of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates generally to a development device which is used in image forming apparatuses, such as copying machines, printers and the like, for developing an electrostatic latent image formed on an image bearing member. In particular, the invention relates to a development device which is arranged such that a developer carrying member for holding a toner thereon and the image bearing member with the electrostatic latent image formed thereon oppose each other across a predetermined gap therebetween and an alternating voltage is applied to the gap for supplying the toner from the developer carrying member to the image bearing member, the development device adapted to produce the image which does not suffer a significant variations in image density or has a stable image density even if the gap between the developer carrying member and the image bearing member varies.
2. Description of the Related Art
The image forming apparatuses, such as the copying machines and printers, have heretofore employed various types of development devices for development of the electrostatic latent images formed on the image bearing members. The known development devices include those utilizing the two component developer comprised of a carrier and a toner, and those utilizing the single component developer free from the carrier.
As the development device of the single component development system, there have been known a contact type development device arranged such that the developer carrying member comes into contact with the image bearing member at a development zone and introduces the developer to the development zone for developing the latent image, and a non-contact type development device arranged such that the developer carrying member opposes the image bearing member across a predetermined gap therebetween and introduces the developer to the development zone opposite to the developer carrying member, thereby accomplishing the development of the latent image.
The contact type development device features an excellent reproducibility of the electrostatic latent image formed on the image bearing member because the latent image is developed by bringing the developer into contact with the image bearing member. However, the developer also adheres to a non-image area of the image bearing member so that the produced image suffers fogging.
Hence, the prior-art development device is designed to prevent the developer from adhering to the non-image area by varying a moving speed of the image bearing member from that of the developer carrying member.
In as much as the contact-type development device has the developer carrying member pressed against a surface of the image bearing member at a given pressure, the developer carrying member moving at the different speed relative to the image bearing member causes abrasion of the surface of the image bearing member. Consequently, the production of images with a stable density is not ensured.
In the non-contact type development device with the developer carrying member opposing the image bearing member across the predetermined gap therebetween, the surface of the image bearing member is not abraded by the developer carrying member. However, significant density variations of the produced images result from the varied gap, at development zone, defined by the developer carrying member and the image bearing member in opposing relation. In a case where a minor variation in the gap between the image bearing member and the developer carrying member results from poor forming precisions of the image bearing member and the developer carrying member, for example, the produced images suffer density variations. Hence, the images with a stable density cannot be obtained.